This invention relates to a fingerprint identification apparatus and more particularly, to an apparatus for enhancing the identification performance by reducing noises produced during the process of fingerprint identification, and facilitating the process of manufacturing and assembly.
In general, there are two ways to identify a fingerprint, i.e., identifying a fingerprint by imaging only light totally reflected from the valley areas of a fingerprint, and by imaging only light diffused from the ridge areas of a fingerprint.
As shown in FIG. 1, a conventional and widely used fingerprint identification apparatus includes a rectangular prism 3 on which a fingerprint is placed for identifying the fingerprint, a multiple LED 2 for radiating light to the fingerprint, an imaging lens 4 for forming images in response to the light totally reflected from the valley areas of the fingerprint, a CCD (Charge Coupled Device) 5 for converting the image to an electrical signal after the image has been formed by the imaging lens 4, a signal processing circuit 6 for analyzing and processing the electrical signal received from the CCD 5, and a select switch 7 for activating the signal processing curcuit 6.
This type of conventional fingerprint identification apparatus is operated by first putting the fingerprint on the oblique plane of the rectangular prism 3. The select switch 7 is then pushed "ON", and the light radiated from the multiple LED 2 is reflected on the valley areas of the fingerprint. Therefore, an image is formed by the imaging lens 4, the image is converted to an electrical signal by the CCD 5 and transmitted to the signal processing circuit 6, and the signal processing circuit 6 identifies the fingerprint.
However, in the conventional fingerprint identification apparatus, the space between each of the LED chips 8 of the multiple LED 2 causes generally inconsistent intensity of radiation as shown in FIG. 3. Thus, it is difficult to obtain a clear image. In order to compensate for this problem, the conventional apparatus must be assembled to maintain a regular distance d from the rectangular prism 3, as illustrated in FIG. 1.
In addition, as shown in FIG. 2, when the fingerprint is placed on the rectangular prism 3 made from a solid material such as glass, a noise is produced because total reflection results from microgaps existing in the ridge areas r of the fingerprint, and the noise causes difficulties in identifying the image of the ridge and the valley areas of the fingerprint. To prevent these noises, generally, the surface of the commonly used rectangular prism 3 is coated with an elastic layer 9 of silicone of a regular thickness.
Also, the conventional apparatus described above has the following deficiencies.
Whenever an identification of the fingerprint is required, the select switch 7 must be operated for activating the signal processing circuit 6 in order to obtain the image of the fingerprint in every case. In addition, the assembling of the apparatus is difficult because the regular space must be maintained between the rectangular prism 3 and the multiple LED 2 to compensate for the inconsistent intensity of radiation according to the characteristics of the multiple LED 2. In cases where foreign substances such as dust exists between the rectangular prism 3 and the multiple LED 2, it is difficult to identify the fingerprint image because of the noises caused by the foreign substances.
Also, the fingerprint image formed by the imaging lens 4 and the CCD 5 may be distorted due to noises caused by bubbles existing within the silicone layer 9, coated on the rectangular prism 3 in order to prevent total reflection from the ridge areas of the fingerprint.